Welcome.....Sounds like a project. Go at it slow and sure. The caps are notorious for that problem. I resort to PB Blaster and separately CLR cleaned and lime dissolver. The old metal tanks are junk,,,and you never know what has grown inside them over the years. A cheap fix is a new ABS type....I like the Valtera types better than the white poly ones. The canister sounds like a water filter....WE LOVE PICTURES!
"If it can't be reduced, reused, repaired, rebuilt, refurbished, refinished, resold, recycled or composted
then it should be restricted, redesigned or removed from production."